Multi-channel key switch circuit

ABSTRACT

A series of key switches are provided with individual tone sources. From one end of the series, output signal is applied to a first frequency divider circuit, thence to suitable formants and to the output of the musical instrument. From another point, or points, in the series of key switches, a second output is taken and applied through a second frequency divider circuit; thence to the formants and output circuits. If two key switches are closed at the same time, that switch closest to the series end feeding the first channel determines the tone which will pass through the first channel. Selective means are provided to cause the other tone to pass through the second channel. In this way two tones can be simultaneously applied to the output circuit, i.e., loudspeaker, where previously only a single tone could be sounded at any one time (monophonic tone sounding).

United States Patent [72] Inventors Bradley J. Plunkett 3,260,784 7/1966 Wehrmann 84/ 1.01 Van Nuys; I 3,388,206 6/1968 Sines 84/l.0lX John R. Brand, Northridge, Calif. 2,874,286 2/ 1959 84/B( UX) [21] Appl. No. 650,531 3,395,242 7/1968 84/B(UX) [22] Filed June 30, 1967 3,417,188 12/1968 84/B(UX) [45] Patented Feb. 2, 1971 [73] Assignee Warwick Electronics Inc. 2"."" Exam".1er Eh Lieberman Chicago, L slstant ExammerT. Vezeau a corporation of Delaware Attorney-Warren T. Jessup [54] I-CHANNFL Y SWITCH CIRCUIT ABSTRACT: A series of key switches are provided with inarms, 2 Drawlng Figs.

dividual tone sources. From one end of the series, output [52] US. Cl 84/ 1.08, i al i a lied to a first frequency divider circuit, thence to 4/ 1 l, 4/ suitable formants and to the output of the musicalinstrument. [51] Int. Cl Gl0h l/00, From another point or points, in the series of key witches a G 10h Gloh second output is taken and applied through a second frequen- Of Search cy divider circuit; therice to the forrnants and output circuits 108, 119, 1-22, B, D If two key switches are closed at the same time, that switch closest to the series end feeding the first channel determines [56] Reierences Cited the tone which will pass through the first channel. Selective UNITED STATES PATENTS means are provided to cause the other tone to pass through 2,710,555 6/1955 Martin 84/1.01 the second channel. In this way two tones can be simultane- 3,040,6l2 6/ 1962 Dorf 84/1.08X ously applied to the output circuit, i.e., loudspeaker, where 3,222,447 12/ 1965 Cookerly et al. 84/1.08X previously only a single tone could be sounded at any one time 3,240,857 3/1966 Munch 84/1.08X (monophonic tone sounding).

INPUYS "OM GEN EIAYOIS a'mvmeu l M m 7 I I6DIVIDEI I 37 37 IODIVIDEI PEDAL VOICING CIICU" AMPLIFIER PATENTED FEB 2197! SHE E1 1 BF 2 INPUTS ERO M GENERATORS 8 DIVIDER I6 DIVIDER PULSE AMPLlFlER 6 3 I 7 E d L I E, \L R J11 I K M PEDAL VO| C|NG CIRCUIT PULSE) AMPLIFIER 8' DIVIDER 16' DIVIDER R F. F U P M A FIG.

INVENTOR.

BRADLEY J- PLUN KETT JOHN R. BRAND ATTORNEY PAIENIEI] FEB 2 ISII SIIEEI 2 (IF 2 III IN-PHASE SE N SOR DIVIDER CIRCUITS AMPLIFIER DIVIDER CIRCUITS PEDAL VOICING CIRCUIT AMPLIFIER INVENTOR.

BRADLEY J. PLUNKETT- JOHN R. BRAND ATTORNEY MULTI-CI-IANNEL KEY swrrcrr CIRCUIT BACKGROUND OF THE INVENTION This invention relates to the art of key switching of electric musical instruments, such as electronic organs. More particularly it is in the field of key switching using periodicity change circuits, such as dividers, which by their very nature can receive only one fundamental frequency at any given time. The invention has particular application where the fundamental is in the fon'n of a square wave having many harmonics, which is uniquely adapted for frequency division.

In the past it has been customary to apply a series of square wave tone sources to the divider circuit, through key-operated key switches, in such a way that if more than one key switch is closed, the divider circuit will nonetheless feel or effectively receive only one of the tone source signals. This is necessitated by the fact that the frequency divider circuit cannot usefully receive simultaneously square wave tone signals of more than one frequency at any one time. The result was the creation of various forms of what are known as monophonic tone generating circuits, capable of delivering to the loudspeaker, through the divider, only one tone at a time. Such circuits are usually used in pedal claviers where the tone generators are set to deliver tones in the upper portion of the bass range, which after application to one or more dividers, are lowered a corresponding number of octaves to become 8 and 16 foot pedal tones.

There are occasions when a skillful organist could make effective use of two pedal tones simultaneously. The purpose of this invention is to provide a modification or addendum to the prior art type of monophonic key switching circuit which makes possible the simultaneous sounding of a second pedal tone.

SUMMARY OF THE INVENTION To the conventional series of key switches, there is added a second output line, which takes its tone signals from a different point in the series than the first or primary tone signal taken from one end of the series. This second tone signal is applied through a second and independent divider circuit and thence combined with the (divided) first tone to provide simultaneously two pedal tones to the output of the musical instrument. Means are provided for insuring that the first tone is applied effectively only to the first divider circuit and the second tone only to the second divider circuit.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a composite circuit and block diagram illustrating one form of the invention;

FIG. 2 is a similar diagram illustrating a second form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 11 represents a series of sources of audio frequency electrical signals, such as tone sources for an electronic organ. The fundamental frequency of the sources is customarily graduated in accordance with the chromatic scale, as indicated. Tone signal from the sources 11 is applied to an output circuit 12 by way of a corresponding plurality of key switches 13 and a channel or circuit 14, which includes one or more dividers l6 and 17. The output circuit 12 usually includes formant or voicing circuits l and a volume control potentiometer 18 feeding tone signal through a final amplifier 19 into a loudspeaker 21. The circuit is usually employed as a pedal circuit in which the tones generated in the tone sources 11 are in the treble range and are stepped down one and two octaves by dividers l6 and 17 before being applied to the output circuit 12. The dividers 16 and 17 can usefully accept only monofrequency tones which customarily are in the form of positive going rectangular pulses 22 having a typical excursion from plus .1 volt to plus 8 volts and return.

To insure that only a single tone signal is applied to the dividers 16 and 17, the series of key switches 13 consists of sequentially connected single-pole, double-throw switches, each having a pole 23, an lower normally closed contact 24, and a lower, normally open, contact 25. The upper contacts 25 are connected to the respective tone sources 11. Each pole 23 is connected to the lower contact 24 of the immediately preceding key switch in the series.

From the FIG. it will be seen that, with the key switches 13 connected in sequence as illustrated, only one tone signal can be applied at any one time to the dividers 16 and 17 in the output channel 14. If more than one switch is closed simultaneously, only that switch which is closest to the front end of the series, i.e., to the switch 13a, will apply signal to the channel 14. All other switches in the sequence following the actuated switch are isolated from access to the input of channel 14 by virtue of the opening of the upper or normally closed contact of that actuated switch which is first in the sequence. It will be noted that in FIG. 1 the first of the switches 13a is connected to the lowest of the tones. This arrangement is thus a lowpreference monophonic tone generator in which only the lowest of the depressed key switches of a plurality of switches will be sounded.

The description heretofore given represents the state of the art to which the present invention applies.

In accordance with the present invention, certain additions are made as follows:

In the connection from each tone generator or source 1 l to the respective upper contact 25 of its switch 13 is connected a voltage dropping resistor 28.

If it is not already intrinsic in the circuit, the coupling channel or circuit 14 is provided with an input circuit, preferably in the form of a pulse amplifier shown at 31, which has a nonlinear impedance. The impedance of the input circuit 31 is such that it presents at its input terminal 32 a relatively high input impedance to all tone signals 22 below a predetermined threshold voltage, and a relatively low impedance to signal above that threshold voltage.

Pulse amplifier 31 consists of two transistors 33 and 34. To input signal at 32 the transistor 33 looks like a diode connected to ground, which presents to the input signal an input impedance which is relatively high as long as the signal stays below a predetermined threshold, for example, 0.6 volts. Above this threshold the transistor 33 conducts and presents a relatively low impedance to the input signal. Amplified signal pulses, of frequency determined by whichever switch 13 is closed, is then applied first to the divider l6 and then in cascade to the divider 17, producing three octavely related tones at output points 36, 37, and 38, respectively.

Also in accordance with the present invention, connections are made to each of the key switches 13, specifically to each of the lower, normally closed, contacts 24. Each connection includes a diode 41 having one terminal connected to the lower contact 24 and the other terminal connected to a common line 42 which in turn feeds to the input 32' of a second channel 14, which is substantially identical to the first channel 14. Like channel 14, channel 14 includes a pulse amplifier 31' and a pair of frequency dividers 16 and 17'. The output of the channel 14', like that of 14, is applied to the output circuit 12 and specifically to the pedal voicing circuits 15 which suitably combine the outputs onto a single output lead 47 connected to the pedal volume potentiometer 18.

The diodes 41 are poled to pass signal from the switches 13 to the common output lead 42. Since in this example the generated signals 22 are assumed to be positive going, the diodes are poled as shown to pass positive going signals. Each diode, like the transistors of the circuit 31, has a threshold voltage below which a high impedance is presented and above which a relatively low impedance is presented. Thus, as long as the signal on the lower contact 24 remains below typically .6 volts, only aninsignificant amount of signal will leak through on to the output lead 42. When the signal rises above .6 volt, however, virtually all of the excess above .6 volt is applied through the diode 41 and through the output circuit 14 14'.

As noted, the signal generators 1 I typically generate output pulses rising to approximately plus 8 volts.

OPERATION Operation of the circuit of FIG. 1 will now be described. Let it be assumed that switches 13b and 13c are both in depressed condition at the same time. Tone signal from generator 11b passes through resistance 28b, pole 23bfand thence down the line of normally closed lower contacts 24 to the first pole 23a and into the first channel 14. As noted, the transistor 33 prevents the voltageon its base 32 from rising substantially above .6 volts. The output signal traveling along the sequence of switches from poles 23b and 23a, therefore, does not rise high enough to pass through any of the diodes 41 and pulse amplifier 31' connected in series, since when so connected, a voltage of 1.2 volts is required before channel 14' feels any signal. Thus the signal from generator 11b will be felt only in the channel 14.

Tone signal from the tone source or generator 11c passes through its resistor 28c, switch pole 23c and thence appears on the lower terminal of the diode 410. Since this point is isolated from the input point 32 on which the voltage has dropped to .6 volts, by the actuation of switch 13b, there is initially available on diode 410 the full 8 volt output of the tone source 11c. There is thus more than sufficient voltage to pass through the series-connected diode 41c and pulse amplifier 31', which, as noted, when in series require l.2 volts to pass current. The voltage at the pole 23c, therefore, drops to 1.2 volts, and signal is continuously passed from the tone generator 11c to the second channel 14 and thence to the output circuit 12. Tone signal from 110 cannot penetrate into the first channel 14, because the diodes 41g and 41h are poled against signal from 11c, thus confining it to the common line 42.

Closing of a third switch, e.g. 13d, would present an ambiguous signal to channel 14', but this contingency is ruled out by the fact that organists have only two feet, and organ duets are rarely attempted.

SECOND SPECIES Referring to FIG. 2, a second form of the present invention is shown. In this FIG. 111 represents a series of tone sources substantially identical to the sources 11 of FIG. 1. The output of each tone source 11 is connected to a respective single pole, single-throw key switch 113. The other side of each switch 113 is connected sequentially down the line to the junction points of a series of voltage dropping resistors 71. The low end 132 of the series 71 is connected to the input of a first channel 114, which includes divider circuits 1 16. The forward or input end of the channel 114 is provided with a very high impedance pulse input amplifier 131.

As in the case of FIG. 1, the output 136 from the channel 114 is applied to voicing circuits 115 and thence to a loudspeaker 121. I

The circuit is so designed that the internal resistance of the tone generators 111 is very low compared to the resistance of any one of the resistances 71, and the input impedance of the pulse amplifier 131 is very high compared to 71. Under these circumstances, if say the switch 1131'; is closed, the output of the tone source 1110 will be applied through the lead 132 to the channel 114, thence through the dividers 116, to the loudspeaker 121. If another key switch 113 farther to the left (higher) in the series, i.e. farther away from the end of the series to which the lead 132 is connected, is now closed, for example switch 113b, all the signal voltage generated in lllb will be dissipated in the resistor 71a, because the internal impedance of 111a is very low compared to 71a. Thus, the tone source lllb will have but negligible effect on the channel 1 14, leaving the tone source 111a as. the only source sounding through the loudspeaker 121.

In accordance with the present invention, the opposite end of the series of resistors 71 is connected by. an output conductor 142 to another output channel 114, substantially identical to the channel 114. Under these conditions when both a When only one switch 113 is closed, tone signal from its tone source 111 will pass in both directions through the seriesconnected resistors 71, through both the leads 132 and 142", and hence simultaneously into both channels 114 and 114,.1 There is no assurance that the dividers 11 6 and 116' might not start up out of phase, so that their respective outputs would cancel each other when applied to the formant circuits 115. To preclude this, there is spanned between the two channels 114 and 114', an in-phase sensor 76, which senses when synchronous, in-phase voltages are being received simultaneously by the two high-impedance input circuits 131 and 131'. When the circuit 76 senses that there is such synchronism, it actuates a killer circuit 77, which precludes one of the dividers, e.g., the divider l 16' from operating.

As soon as a second key switch, e.g., 113b, is closed, this simultaneous signal condition no longer exists, inasmuch as the amplifier 131' is now receiving its predominant signal from the source lllb. Under theseconditions, the in-phase sensor 76 no longer operates to disable the divider1 16 via the killer 77, and both signals (of different frequency) now are permitted to pass through their respective channels to the output circuit 112.

Whereas the present invention has been shown and described herein in what is conceived to be the best mode contemplated, it is recognized that departures may be made therefrom within the scope of the invention which is, therefore, not to be limited to the details disclosedherein, but is to be afforded the full scope of the invention as hereinafter claimed. I

We claim:

1. Switching system for an electric music system, comprismg:

a plurality of sequentially connected key switches;

a corresponding plurality of tone sources connected respectively to said key switches;

an output circuit for the system;

first circuit means connecting thefirst of said switches in the sequence to said output circuit, characterized by said first circuit means having a nonlinear input impedance which is relatively high to tone signals when the voltagethereof is below a first predetermined threshold, and relatively low when said voltage is above said threshold;

second circuit means connecting each of said key switches to said outputcircuit" and having a nonlinear input impedance which is relatively high to tone signals below a second predetermined threshold voltage, and relatively low to signals above said threshold voltage, said second threshold voltage being substantially greater than said first threshold voltage; and

the peak voltage of tone signals delivered by said tone sources being greater than said second threshold voltage.

2. Switching system foran electric music system, comprisa plurality of sequentially connected key switches;

a corresponding plurality of tone sources connected respectively to said key switches;

an output circuit connected to the first of said switches in the sequence, characterized by a corresponding plurality of nonlinear irnpedances, each having ojne terminal thereof connected to a respective key switch, and characterized by a relatively high impedance when the voltage thereacross is below a predetermined minimum and a relatively low impedance when such voltage is above said minimum; and

circuit means connecting all the respective other terminals of said impedances to said output circuit.

3. In a key switching circuit for an electric musical instrument, comprising:

a plurality of sequentially arranged, single-pole, doublethrow key switches, each having a pole, a first contact, and a second contact;

a corresponding plurality of electric tone signal sources connected to the respective second contacts of said key switches;

an output circuit including speaker means;

first circuit means including frequency divider means for connecting said output circuit to the pole of the first key switch in the sequence of key switches;

second circuit means for connecting the poles of the remaining key switches respectively to the first contact of the immediately preceding key switch in the sequence, the improvement which comprises providing a plurality of voltage dropping resistors in the respective connections between said tone sources and said second contacts;

providing the input of said first circuit means with a nonlinear impedance which presents a relatively high input impedance to tone signal below a first predetermined threshold voltage and a relatively low input impedance to signal above said first threshold voltage;

third circuit means connected from each of the first contacts of said key switches to said output circuit and including frequency divider means, and a plurality of diodes connected respectively to said first contacts and poled to pass signal from said first contacts to said output circuit;

said third circuit presenting to tone signal applied to said first contacts a nonlinear impedance which is relatively high when signal voltage is below a second predetermined threshold and relatively low when above said second predetermined threshold voltage;

said second threshold voltage being substantially greater than said first threshold voltage; and

the amplitude of signal voltage delivered from said tone sources being above said second threshold voltage.

4. In an electric musical instrument, comprising:

a plurality of sources of audio frequency electric signals;

a corresponding series of key switches;

first circuit means for coupling each switch to a corresponding signal source;

second circuit means for connecting said key switches together;

output circuit means;

first channel circuit means for connecting one end of the series of key switches to said output circuit means, whereby if and when aplurality of key switches are closed simultaneously, only that key switch in the series closest to said one end will effect the application of signal to said output circuit means; and

the improvement which comprises second channel circuit means connected to said second circuit means and to said output circuit means, said second channel means including means for applying signal from a given key switch to said output circuit means only if a key switch closer to said one end than said given key switch is simultaneously closed.

5. The combination of Claim 4, wherein:

said second circuit means comprises a plurality of seriesconnected impedances, said key switches being connected respectively to the junction points between said impedances;

said second channel circuit means comprises circuit means for connecting the opposite end of said series of key switches to said output circuit means; and

means connected to said first and second channel circuit means for inhibiting the signal ap lying o eration of one of said channel circuit means w en on y a single key switch is closed.

6. The combination of Claim 4, wherein:

said first channel circuit means comprises threshold impedance means for passing only audio frequency signals above a first predetermined threshold voltage; and

said second channel circuit means comprises circuit means connected to each of said key switches and includes threshold impedance means for passing only audio frequency signals above a second predetermined threshold voltage higher than said first threshold voltage. 

1. Switching system for an electric music system, comprising: a plurality of sequentially connected key switches; a corresponding plurality of tone sources connected respectively to said key switches; an output circuit for the system; first circuit means connecting the first of said switches in the sequence to said output circuit, characterized by said first circuit means having a nonlinear input impedance which is relatively high to tone signals when the voltage thereof is below a first predetermined threshold, and relatively low when said voltage is above said threshold; second circuit means connecting each of said key switches to said output circuit and having a nonlinear input impedance which is relatively high to tone signals below a second predetermined threshold voltage, and relatively low to signals above said threshold voltage, said second threshold voltage being substantially greater than said first threshold voltage; and the peak voltage of tone signals delivered by said tone sources being greater than said second threshold voltage.
 2. Switching system for an electric music system, comprising: a plurality of sequentially connected key switches; a corresponding plurality of tone sources connected respectively to said key switches; an output circuit connected to the first of said switches in the sequence, characterized by a corresponding plurality of nonlinear impedances, each having one terminal thereof connected to a respective key switch, and characterized by a relatively high impedance when the voltage thereacross is below a predetermined minimum and a relatively low impedance when such voltage is above said minimum; and circuit means connecting all the respective other terminals of said impedances to said output circuit.
 3. In a key switching circuit for an electric musical instrument, comprising: a plurality of sequentially arranged, single-pole, double-throw key switches, each having a pole, a first contact, and a second contact; a corresponding plurality of electric tone signal sources connected to the respective second contacts of said key switches; an output circuit including speaker means; first circuit means including frequency divider means for connecting said output circuit to the pole of the first key switch in the sequence of key switches; second circuit means for connecting the poles of the remaining key switches respectively to the first contact of the immediately preceding key switch in the sequence, the improvement which comprises providing a plurality of voltage dropping resistors in the respective connections between said tone sources and said second contacts; providing the input of said first circuit means with a nonlinear impedance which presents a relatively high input impedance to tone signal below a first predetermined threshold voltage and a relatively low input impedance to signal above said first threshold voltage; third circuit means connected from each of the first contacts of said key switches to said output circuit and including frequency divider means, and a plurality of diodes connected respectively to said first contacts and poled to pass signal from said first contacts to said output circuit; said third circuit presenting to tone signal applied to said first contacts a nonlinear impedance which is relatively high when signal voltage is below a second predetermined threshold and relatively low when above said second predetermined threshold voltage; said second thrEshold voltage being substantially greater than said first threshold voltage; and the amplitude of signal voltage delivered from said tone sources being above said second threshold voltage.
 4. In an electric musical instrument, comprising: a plurality of sources of audio frequency electric signals; a corresponding series of key switches; first circuit means for coupling each switch to a corresponding signal source; second circuit means for connecting said key switches together; output circuit means; first channel circuit means for connecting one end of the series of key switches to said output circuit means, whereby if and when a plurality of key switches are closed simultaneously, only that key switch in the series closest to said one end will effect the application of signal to said output circuit means; and the improvement which comprises second channel circuit means connected to said second circuit means and to said output circuit means, said second channel means including means for applying signal from a given key switch to said output circuit means only if a key switch closer to said one end than said given key switch is simultaneously closed.
 5. The combination of Claim 4, wherein: said second circuit means comprises a plurality of series-connected impedances, said key switches being connected respectively to the junction points between said impedances; said second channel circuit means comprises circuit means for connecting the opposite end of said series of key switches to said output circuit means; and means connected to said first and second channel circuit means for inhibiting the signal applying operation of one of said channel circuit means when only a single key switch is closed.
 6. The combination of Claim 4, wherein: said first channel circuit means comprises threshold impedance means for passing only audio frequency signals above a first predetermined threshold voltage; and said second channel circuit means comprises circuit means connected to each of said key switches and includes threshold impedance means for passing only audio frequency signals above a second predetermined threshold voltage higher than said first threshold voltage. 